This invention relates to a thermal (heat-sensitive) transfer recording medium, more specifically it relates to a thermal transfer recording medium which can provide a good printing quality to a paper to be transferred and can use effectively even in a small device which is small in winding torque.
Recently, a thermal transfer recording system using a thermal transfer recording medium has been attracted attention.
The thermal transfer recording system is a method in which, on a sheet-like support, by using a thermal recording medium which is being provided thereon a thermal transfer colorant layer comprising by dispersing a colorant in a heat-fusible substance and/or thermal plastic resin, an ink image which corresponds to heated portions of a thermal head is formed on the medium to be transferred by heating the thermal transfer colorant layer from the support side of the thermal recording medium with use of the thermal head at the state of contacting with a medium to be transferred (generally, a paper) to fuse (or soften) the thermal transfer colorant layer whereby transferring the layer to the medium to be transferred.
The thermal transfer recording medium to be used in this method is generally used in the state of being contained in a cassette.
The thermal transfer recording medium having such a state is wounded in the cassette at the condition that the thermal transfer colorant layer and a back surface of the support are contacted with each other. When it has been stored at that condition for a long term, a part of the heat fusible substance, etc. of the thermal transfer colorant layer becomes a fused state, and will sometimes cause an adhesion strength between the back surface of the support and the surface of the thermal transfer colorant layer. This adhesion strength is, in usual case, not so strong so that it was not a serious problem in the large scale apparatus conventionally used.
However, in accordance with development of a small size apparatus at the latest days, it has been found that the adhesion strength thus appeared causes a large effect to the transferring property. That is, since the small size apparatus (for example, a portable word processor, etc.) is small in driving force for running of the thermal transfer recording medium, running property of the thermal transfer recording medium is sometimes lowered even due to a little adhesive strength and such a case, transferring property is remarkably lowered. Also, when the thermal transfer recording medium is to be run, if the thermal transfer colorant layer has adhesive property, it also lowers in the running property since it contacts with support pole, etc.
Thus, in order to solve such problems, there is described a thermal transfer recording medium in which a specific amount of silicone oil has been added in Japanese Provisional Patent Publication No. 139489/1986.
However, the silicone oil used in this invention has a dimethylpolysiloxane structure, and according to the present inventors' investigation, the silicone oil having such a structure is low in compatibility with a heat-fusible substance and/or a thermal plastic resin, etc. which are main components of a thermal transfer colorant layer, and therefore, it can be found that it is difficult to uniformly disperse the silicone oil in the thermal transfer colorant layer. Further, it can be found that the silicone oil having such an unmodified dimethylpolysiloxane structure is insufficient in lubricating property as a lubricating component of a thermal transfer recording medium used in a small apparatus.
Also, in Japanese Provisional Patent Publication No. 263796/1986, an invention of a thermal transfer recording medium in which a solid ink layer contains a liquid modified silicone oil.
Thus, running properties of the thermal transfer recording medium are somewhat improved by using a modified silicone oil but it could not be said that it has been not yet sufficient. Further, even if the modified silicone oil has been used, printing quality to a medium to be transferred which is low in surface smoothness, which has recently been often used in the aforesaid portable word processor, is almost the same as before.